1. Field of the Invention
This invention generally relates to digital image processes and, more particularly, to a system and method for limiting the volume of image information that is compressed when a camera with automatic gain control is operated near, or at full gain.
2. Description of the Related Art
The digital compression of images is becoming more and more popular with the rise of Internet and other bandwidth limited communications channels. There are currently many applications where images are being captured with a CCD, CMOS, or an analog output camera, digitized, compressed, and either sent live to recipients, or stored for future use.
Most conventional cameras implement an automatic gain control feature that permit images to be captured in varying light conditions. Unfortunately, when the gain is near, or at maximum gain, a certain amount of video noise is introduced to the captured image. Compression algorithms are less effective when an image contain a large amount of random noise. When compressed, the resulting output file is very large and contains noise as well as image information. The creation of the additional volume of compressed data is process intensive, without the benefit of adding useful information. In applications where the storage capacity or the bandwidth used to send the series of images through a communication channel is a precious commodity or is otherwise limited, the system suffers with increased storage requirements or communication delays without a corresponding benefit.
For example, when a video camera with automatic gain control and compression is deployed to record real-time images in an outdoor location, the output data initially consists of high quality images with little or no noise, and the compression ratio is high. As darkness falls, the camera gain increases to adapt to the new lighting conditions. The increase in camera gain results in an increase of video noise in the image, causing the compression ratio to drop and the size of the compressed data to grow. The increase in the amount of compressed data impacts storage requirements and communication delay without improving the image quality.
It is known for digital imaging processing equipment to implement image correction algorithms, or to adjust compression parameters in response to an analysis of the captured image information. However, such image analysis processes are computationally intensive and difficult to implement in real-time with economy.
It would be advantageous if a low-light compensation algorithm could be implemented without resort to a complex analysis of the image information.
It would be advantageous if the amount of digital image information that is compressed could be limited as a digital camera gain approaches the maximum value.